In recent years, lithium ion batteries, nickel hydride batteries, and other secondary batteries have become increasingly important as power sources for mounting in vehicles using electricity as a driving source, and as power sources installed in personal computers, portable terminals, and other electronic products and similar. In particular, lithium ion batteries, which are lightweight and can achieve high energy densities, are regarded favorably as high-output power sources for mounting in vehicles.
One mode of such batteries is a sealed battery in which a prescribed electrode unit and electrolyte are accommodated within a case. Typically in construction of such a sealed battery, after an electrode unit comprising the positive electrode and the negative electrode is accommodated by a metal case, a lid is installed in the opening portion of the case (that is, the accommodating opening which accommodates the electrode unit), to perform sealing.
As sealing means used in this type of battery, various methods are available. Typically, laser welding employing a YAG laser, CO2 laser, or other heat source is often used. In particular, laser welding enables the selective and local application of heat, and so is preferred. However, there are concerns that on rare occasions sputtered material may fly into gaps within the case and result in internal short-circuits or similar.
Also, the surface of the lid opposing the case (the surface at which the inside of the case is positioned when installed in the case opening portion) has a portion which enters into the case opening portion (hereafter called the “inside protruding portion”) in order to prevent welding defects and to prevent shifts in position of the lid, but this inside protruding portion of the lid may be formed in a shape which makes close contact with the peripheral wall portion of the case when the lid is installed in the case opening portion, that is, a shape such that there exists no gap (clearance) between the inside protruding portion of the lid and the periphery of the case opening portion. However, in such a state with no clearance, if the relative positions of the lid and the case opening portion when installing the lid in the case opening portion are not correct, and a shift in positions occurs, then there are concerns that the inside edge (that is, the opening portion periphery) of the opening end portion of the case peripheral wall portion and the inside protruding portion of the lid may grind together powerfully, and that “galling” may occur. The occurrence of “galling” may cause the inclusion of metal particles (that is, shaved particles) arising from this shaving within the case, resulting in internal short-circuits and similar, and so is undesirable.
Examples of related technologies of this type are described in Patent Documents 1 through 4. In the technology described in Patent Document 1, by coating the entirety of the outside walls of the outer receptacle (case) of the battery with a protective film, the occurrence of shaving which is possible during lid installation is suppressed. And in the technologies of Patent Documents 2 through 4, disclosures are made relating to the shapes of the mating portions of the case and lid so as to enable suppression of internal short-circuits due to flying sputtered material.
However, according to Patent Document 1, shaved particles which tend to occur at the time of installation of the lid on the case opening portion are suppressed, but because at the time of welding the surface irradiated with laser light is also covered with the protective film, the metals comprised by the case and lid are insufficiently melted, and there are concerns that welding defects may occur. And, in Patent Documents 2 through 4, flying sputtered material can be suppressed, but in all these cases it is difficult to suppress the occurrence of shaved particles.
Patent Document 1: Japanese Patent Application Laid-open No. 2005-71710
Patent Document 2: WO99/25036
Patent Document 3: Japanese Patent Application Laid-open No. 2002-279944
Patent Document 4: Japanese Patent Application Laid-open No. 11-162419